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      1 /*
      2  ** Copyright 2003-2010, VisualOn, Inc.
      3  **
      4  ** Licensed under the Apache License, Version 2.0 (the "License");
      5  ** you may not use this file except in compliance with the License.
      6  ** You may obtain a copy of the License at
      7  **
      8  **     http://www.apache.org/licenses/LICENSE-2.0
      9  **
     10  ** Unless required by applicable law or agreed to in writing, software
     11  ** distributed under the License is distributed on an "AS IS" BASIS,
     12  ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  ** See the License for the specific language governing permissions and
     14  ** limitations under the License.
     15  */
     16 
     17 /***********************************************************************
     18 *      File: hp50.c                                                     *
     19 *                                                                       *
     20 *      Description:                                                 *
     21 * 2nd order high pass filter with cut off frequency at 31 Hz.           *
     22 * Designed with cheby2 function in MATLAB.                              *
     23 * Optimized for fixed-point to get the following frequency response:    *
     24 *                                                                       *
     25 *  frequency:     0Hz    14Hz  24Hz   31Hz   37Hz   41Hz   47Hz         *
     26 *  dB loss:     -infdB  -15dB  -6dB   -3dB  -1.5dB  -1dB  -0.5dB        *
     27 *                                                                       *
     28 * Algorithm:                                                            *
     29 *                                                                       *
     30 *  y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2]                         *
     31 *                   + a[1]*y[i-1] + a[2]*y[i-2];                        *
     32 *                                                                       *
     33 *  Word16 b[3] = {4053, -8106, 4053};       in Q12                      *
     34 *  Word16 a[3] = {8192, 16211, -8021};       in Q12                     *
     35 *                                                                       *
     36 *  float -->   b[3] = {0.989501953, -1.979003906,  0.989501953};        *
     37 *              a[3] = {1.000000000,  1.978881836, -0.979125977};        *
     38 ************************************************************************/
     39 
     40 #include "typedef.h"
     41 #include "basic_op.h"
     42 #include "oper_32b.h"
     43 #include "cnst.h"
     44 #include "acelp.h"
     45 
     46 /* filter coefficients  */
     47 static Word16 b[3] = {4053, -8106, 4053};  /* Q12 */
     48 static Word16 a[3] = {8192, 16211, -8021}; /* Q12 (x2) */
     49 
     50 /* Initialization of static values */
     51 
     52 void Init_HP50_12k8(Word16 mem[])
     53 {
     54     Set_zero(mem, 6);
     55 }
     56 
     57 
     58 void HP50_12k8(
     59         Word16 signal[],                      /* input/output signal */
     60         Word16 lg,                            /* lenght of signal    */
     61         Word16 mem[]                          /* filter memory [6]   */
     62           )
     63 {
     64     Word16 x2;
     65     Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1;
     66     Word32 L_tmp;
     67     Word32 num;
     68 
     69     y2_hi = *mem++;
     70     y2_lo = *mem++;
     71     y1_hi = *mem++;
     72     y1_lo = *mem++;
     73     x0 = *mem++;
     74     x1 = *mem;
     75     num = (Word32)lg;
     76     do
     77     {
     78         x2 = x1;
     79         x1 = x0;
     80         x0 = *signal;
     81         /* y[i] = b[0]*x[i] + b[1]*x[i-1] + b140[2]*x[i-2]  */
     82         /* + a[1]*y[i-1] + a[2] * y[i-2];  */
     83         L_tmp = 8192 ;                    /* rounding to maximise precision */
     84         L_tmp += y1_lo * a[1];
     85         L_tmp += y2_lo * a[2];
     86         L_tmp = L_tmp >> 14;
     87         L_tmp += (y1_hi * a[1] + y2_hi * a[2] + (x0 + x2) * b[0] + x1 * b[1]) << 1;
     88         L_tmp <<= 2;           /* coeff Q12 --> Q13 */
     89         y2_hi = y1_hi;
     90         y2_lo = y1_lo;
     91         y1_hi = (Word16)(L_tmp>>16);
     92         y1_lo = (Word16)((L_tmp & 0xffff)>>1);
     93         *signal++ = extract_h((L_add((L_tmp<<1), 0x8000)));
     94     }while(--num !=0);
     95 
     96     *mem-- = x1;
     97     *mem-- = x0;
     98     *mem-- = y1_lo;
     99     *mem-- = y1_hi;
    100     *mem-- = y2_lo;
    101     *mem-- = y2_hi;
    102 
    103     return;
    104 }
    105 
    106 
    107